Many people with Twitter law degrees are commenting on whether the armed St. Louis couple were justified in defending their "private property" under the castle doctrine. As an actual criminal law professor, I thought I should clear up some confusion. 1/

At first glance, the text of MO's self-defense rule seems quite broad. https://revisor.mo.gov/main/OneSection.aspx?section=563.031&bid=33873&hl=

"A person shall not use deadly force … unless … [s]uch force is used against a person who unlawfully enters, remains after unlawfully entering, or attempts to unlawfully enter private property that is owned or leased by an individual…"

Whereas the large majority of jurisdictions limit the castle doctrine to the boundaries of the house, MO's is more expansive. Some commenters are reading the statute to mean that you could lawfully shoot someone who stepped onto your lawn.

Despite the availability of signs saying "Trespassers will be shot," mere trespass has not historically been a basis for using deadly force. So, does MO's statute represent a new trend, allowing expansive use of deadly force to protect private property? No.

The "private property" clause is limited by other sections of the self-defense statute. A MO appellate court, in State v. Whipple, 501 S.W.3d 506 (2016) explained:

"an owner or lessee of private property ("the owner or lessee") is entitled to use deadly force to repel an unlawful entry, but only if he meets the requirements of self-defense set out in section 563.031.1" So what are the requirements of 563.031.1? Here is the statute:

"A person may ... use physical force upon another person when and to the extent he or she reasonably believes such force to be necessary to defend himself or herself or a third person from what he or she reasonably believes to be the use or imminent use of unlawful force..."

There are three exceptions to that clause combined with an initial aggressor limitation, but none apply in this case. MO's statute is bit of a mess, but that's quite typical of self-defense statutes across the country. The Whipple court concluded:

"we cannot find that subsection 3 gives the occupier, owner, or lessee authority to stand his ground and use deadly force without having a reasonable belief that such force is necessary to defend himself or a third person from what he reasonably believes to be the use or (cont.)

imminent use of unlawful force."

Be careful taking 1 clause out of a statute and interpreting it alone.

tldr: MO law does not allow deadly force to be used to merely defend private property (excepting the home itself).
/end